Hemp Insulation in timber frame

[Thorfun]

Hi all,

we're currently in the plan drawing phase with the architect for our West Sussex project. We're trying to get away from using oil based products in the build and I am drawn towards using hemp for the insulation of the house.

The architect has said that the calculations to get wall U values of around 0.15 with hemp we would need at least 400mm thick walls.

We'd rather not lose that much internal space if possible so we're investigating a potential hybrid solution where we use hemp in the timber frame walls and then cover it in another insulation to obtain the required levels. he has suggested we look at the Actis products. I remember reading about the debunked claims on their old product (and have read through old threads on here about the multi-foil insulation) and am a bit sceptical but by using it as a secondary layer and it being so easy to fit that I could do it myself is quite a tempting solution.

so, I guess my question to the forum is has anyone used hemp as an insulation material? can anyone think of a different (preferably non-oil based product) that could be used as a secondary layer to reduce the cold-bridging from the timber frame that isn't Actis? or can anyone suggest that Actis have got their act together and now have a product that is worth using? he was talking about the hcontrol hybrid Actic product with the built in vapour control.

thanks in advance.

[Stewpot]

 .

Edited January 15, 2020 by Stewpot
Pressed wrong button

[ProDave]

I Knauf Earthwool  Frametherm 35.  It's a glass wool variant that is a LOT less nasty to handle than some of the glasswool types.

 

I don't know how much if any oil it uses in manufacture.

 

My neighbour used hemp as one layer of his insulation, I remember it was both expensive and not a particularly good insulator.

[Stewpot]

1 hour ago, Thorfun said:

...has anyone used hemp as an insulation material?

 

Not yet, but I do find it an attractive idea. I'm half way through reading The Hempcrete Book. Are you planning cast-in-situ?

 

The book lists typical U-values as follows:

 

Wall thickness:               250mm               300mm               350mm               400mm

            U-value:             0.23W/m²K        0.2W/m²K         0.17W/m²K        0.15W/m²K

 

Apparently there are quilts which have higher performance, and also pre-cast blocks and panels, but I couldn't comment about these.

 

I'm hunting around for a training course, to see if I can learn more.

[Thorfun]

17 hours ago, ProDave said:

I Knauf Earthwool  Frametherm 35.  It's a glass wool variant that is a LOT less nasty to handle than some of the glasswool types.

 

I don't know how much if any oil it uses in manufacture.

 

My neighbour used hemp as one layer of his insulation, I remember it was both expensive and not a particularly good insulator.

 

Hi Dave. thanks for the information on the Earthwool. I'll look in to that.

I know that hemp isn't the best insulator. The Thermafleece Natrahemp product has a Thermal conductivity of 0.040 whereas PIR seems to have a thermal conductivity of around 0.023, hence the thick walls to get a similar level of insulation. 

some of our sustainability requirements will need to be dropped as we price up the build and it may end up being insulation but I'd like to at least investigate all options before we make a decision!

[Thorfun]

17 hours ago, Stewpot said:

 

Not yet, but I do find it an attractive idea. I'm half way through reading The Hempcrete Book. Are you planning cast-in-situ?

 

The book lists typical U-values as follows:

 

Wall thickness:               250mm               300mm               350mm               400mm

            U-value:             0.23W/m²K        0.2W/m²K         0.17W/m²K        0.15W/m²K

 

Apparently there are quilts which have higher performance, and also pre-cast blocks and panels, but I couldn't comment about these.

 

I'm hunting around for a training course, to see if I can learn more.

 

I was thinking about simply getting Hemp batts and fitting them between the stud work of the timber frame.

 

on the Black Mountain website their NatuHemp product has the following U-values:

 

THERMAL PERFORMANCE
Thickness	Thermal Resistance (R)	U Value
50mm	1.28 m2k/W	0.76 W/m2K
75mm	1.92 m2k/W	0.52 W/m2K
100mm	2.56 m2k/W	0.39 W/m2K
150mm	3.85 m2k/W	0.26 W/m2K
200mm	5.13 m2k/W	0.20 W/m2K
250mm	6.14 m2k/W	0.16 W/m2K

 

interestingly, according to the Kingspan U-value calculator 120mm of their K12 framing board with the following build-up yields a 0.23 W/m2K U-value so similar to the 150mm of hemp. And both require further insulation to get to a decent U-value.

Construction build-up includes:

• 3mm skim coated 15mm plasterboard
• Polythene vapour control layer
• Kingspan Kooltherm K12 Framing Board between timber studs
• 9mm OSB
• Kingspan nilvent breathable membrane
• Timber cladding on battens.

I need to do a LOT more research on the whole subject and would value other opinions on the subject.

 

[Patrick]

Hemp is quite expensive AFAIK and not really the greatest insulation product. If you want something natural and organic it's probably better to use sheep wool.

Loads on here, incl myself, are using blown in cellulose, alternatively blown in wood fibre. Both fairly good insulation, quite cheap, and low poisoning. I wanted something that apart from easy installation, price, also has little off gasping and is potentially the least poisonous

[Thorfun]

5 minutes ago, Patrick said:

Hemp is quite expensive AFAIK and not really the greatest insulation product. If you want something natural and organic it's probably better to use sheep wool.

Loads on here, incl myself, are using blown in cellulose, alternatively blown in wood fibre. Both fairly good insulation, quite cheap, and low poisoning. I wanted something that apart from easy installation, price, also has little off gasping and is potentially the least poisonous

 

Hi Patrick. 

thanks for the response. I am considering blown in cellulose as a potential option as well although that's not something that I can fit myself.

at least with hemp batts I can fit them myself and save some money (as well as do my bit for the planet). although I guess a counter argument to saving money by self-fitting is that the money I would save by using blown cellulose would pay for someone to do it for me!

so much to research and I've only just started!

[ADLIan]

The U-value table from Black Mountain is meaningless. U-values apply to the whole build up, including all individual elements, of the floor, wall or roof. Additionally with timber frame it does not account for 15% thermal bridging of the insulation - the Kingspan figure does. Looking at insulation in isolation the hemp has a thermal conductivity of 0.039 W/mK compared to 0.018 (?) W/mK for Kingspan. The simple ratio of these 2 values shows you need twice the thickness of hemp to equate to the Kingspan product.

 

Mineral wool is normally the product of choice here for ease of use and robustness of install, has good 'eco' credential and not oil based.

 

[Thorfun]

26 minutes ago, ADLIan said:

The U-value table from Black Mountain is meaningless. U-values apply to the whole build up, including all individual elements, of the floor, wall or roof. Additionally with timber frame it does not account for 15% thermal bridging of the insulation - the Kingspan figure does. Looking at insulation in isolation the hemp has a thermal conductivity of 0.039 W/mK compared to 0.018 (?) W/mK for Kingspan. The simple ratio of these 2 values shows you need twice the thickness of hemp to equate to the Kingspan product.

 

Mineral wool is normally the product of choice here for ease of use and robustness of install, has good 'eco' credential and not oil based.

 

 

thanks for the great information and the 'twice the thickness' simplicity makes perfect sense. so, unless I want really thick walls hemp is not really the way to go is what I'm getting from the responses so far!

 

I will definitely look in to mineral wool. cheers.

[joe90]

If I were building timber frame I would use blown cellulose like @Jeremy Harris very good for air tightness and decrement delay as well. His blog is a mine of information.

[Thorfun]

24 minutes ago, joe90 said:

If I were building timber frame I would use blown cellulose like @Jeremy Harris very good for air tightness and decrement delay as well. His blog is a mine of information.

 

yep! I've read it which is why blown cellulose is on the list of considerations. ?

 

 

[Thorfun]

this was an interesting read (https://www.ecomerchant.co.uk/news/insulation-materials-compared/) that someone posted in another thread.

 

it seems that maybe wood fibre might be the way to go as it has a lower lambda value and decrement delay value.

 

more research is required! ?

[Jeremy Harris]

Wood fibre is pretty good stuff, IMHO.  Essentially similar to cellulose (both come from the same source).  Nicer to handle than a lot of other fibrous products, too, and it is reasonably good as acoustic insulation.

[Thorfun]

I'm wondering if I can use flexible wood fibre between the timber frame and then the rigid wood fibre sheathing on the outside as further insulation and air tightness and attach the timber cladding to the sheathing? 

 

obviously, I'm only just starting on my journey so something like that might not actually be possible for various/numerous reasons!

[Patrick]

1 hour ago, Thorfun said:

I'm wondering if I can use flexible wood fibre between the timber frame and then the rigid wood fibre sheathing on the outside as further insulation and air tightness and attach the timber cladding to the sheathing? 

 

obviously, I'm only just starting on my journey so something like that might not actually be possible for various/numerous reasons!

I was looking into exactly the same but stayed away from it.

1. Woodfibre boards are expensive (blown in Woodfibre isn't, unless you buy it from an eco-merchant which will put 150% margin on top cause its eco)

2. Fixing them and then outside cladding is another step, extra work, extra trouble.

 

I decided to rather increase the size of the walls and eliminate the thermal bridging (as far as reasonable) . can be done like @Jeremy Harris

 and others done, with MBC frame, who are using some sort of Larsen Truss, or others like@Simplysimon

Using i-beams (me as well).

 

There are a few advantages in the blown in insulation over rolls, boards or sheets

 

Mentioned plenty of times:

-it will get in every corner and have a tight fit.

 

Too much of other types of insulation are down to your or the installers fitting skills.

 

I believe the blown in is also a bit of a time saver as its quicker installed.

 

Alternatively you could use spray foam and get the same pros than blown in insualtion, but for me it wasn't right as I don't trust the chemistry of it. It s not tested long enough for me to be sure that it's safe (somebody - asbestos?)

 

I think if you have the space, straw insualtion could work excellent, and in case you got a sheep farm, wool works very well, but in all other cases there really is a strong argument for blown in insualtion.

[Thorfun]

thanks Patrick for the response. all great information!

 

I've not actually looked at the prices of this stuff yet. once I get the final dimensions of the external walls I'll put it all in a spreadsheet and calculate the cost differences between them all.

 

I assume that with the blown cellulose there are 3rd party companies that will perform the work after a timber frame has been erected? or are you limited to a timber frame company that offers it as a solution?

[jamieled]

1 hour ago, Thorfun said:

I assume that with the blown cellulose there are 3rd party companies that will perform the work after a timber frame has been erected? or are you limited to a timber frame company that offers it as a solution?

Yep, that's what we're doing. PYC (Warmcel distributors) can help you arrange quotes from installers and check your wall build up is suitable by running condensation calcs etc.

 

There may well be other blown cellulose producers who do similar though.

[Thorfun]

so, I've been looking further in to this, specifically with regard to prices to compare our different options and must be doing something wrong! it appears that the Kingspan K12 framing board is the most expensive insulation when priced per m2 and compared to hemp, wood fibre and loose cellulose (just for the product and not including installation). 

 

 

 

please tell me I'm wrong here. I thought the PIR insulation was cheaper than eco products? or am I being naive here and you're actually paying a premium for thin insulation (and thus thinner walls)? 

 

if this is the case then I think I'd rather lose space from my room size and buy a cheaper and more eco friendly product.

 

Edited January 22, 2020 by Thorfun
formatting issue

[Thorfun]

actually, now I think about it, to get similar U-values I'll need double the thickness of eco insulation so the I need to double those prices so the Kingspan isn't actually as more expensive than I first thought.

 

sorry. schoolboy newbie error! ?‍♂️

[A_L]

@Thorfun , for the same thermal resistance PIR/PUR is typically twice the price of mineral wool batts

[Thorfun]

8 minutes ago, A_L said:

@Thorfun , for the same thermal resistance PIR/PUR is typically twice the price of mineral wool batts

 

ok, twice the price for half the thickness. I guess that makes sense.

[A_L]

17 minutes ago, Thorfun said:

 

ok, twice the price for half the thickness. I guess that makes sense.

 

no, twice the price for the same insulating effect

[Thorfun]

11 minutes ago, A_L said:

 

no, twice the price for the same insulating effect

now I'm even more confused!

but that same insulating effect will be twice as thick to get the same U-value, right?

[A_L]

4 minutes ago, Thorfun said:

but that same insulating effect will be twice as thick to get the same U-value, right?

 

mineral wool batts will typically have a thermal conductivity of 0.035 W/m.K and PIR 0.022W/m.K. Thus 22mm of PIR will have the same insulating effect as 35mm of batt

 

steico wood fibre batts, IIRC with a thermal conductivity of 0.048W/m.K will have the same insulating effect at 48mm thickness